Extrude and subdivide without using tris
Here are a couple of ways to increase vertex count between edge loops using all quads.



And a quick trick for the right one using inset.


Set face select mode
Select two faces at the end you want to expand loop cuts.
Press I and inset a small amount 
Select next two faces and press Shift R
Repeat step 4
Select all new internal faces 
press Shift R
repeat 6 and 7 a few times 
Set vertex select mode and box select the bottom vertices and delete




If you have a fully round mesh like your dress you can get around this step if you apply the mirror modifier and disable boundary in the inset options when doing the first inset. You can then delete half the dress and re-add the mirror modifier.

I now have a mesh that starts with 5 vertices at the top and ends with 37 at the bottom.